Process for manufacturing heat-insulated castings

ABSTRACT

The present disclosure relates to a process for manufacturing cast pipes of the type which excel in heat-insulating characteristics and which are highly durable under high temperatures. An internal core of metallic material with high resistance to heat and corrosion is externally coated with a highly heat-insulating layer to thereby produce a double structure, and the double structure is then surrounded in molten metal to produce the casting.

United States Patent 1191 Niimi et a1.

[ Feb. 4, 1975 [54] PROCESS FOR MANUFACTURING 938,688 11/1909 Nichols 164/75 HEATJNSULATED CASTINGS 938,689 11/1909 Nichols 164/75 1,025,817 5/1912 Luckenbach 164/100 1 Inventors: Itarll b y Yasuhlsa 2,690,004 9/1954 Crawford 164/111 Kaneko, Toyota; Akiyoshi Morita, 3,170,452 2/1965 Dobovan 164/102 Toyota; Katumi Yagi, Toyota; 3,173,451 3/1965 Slayter 138/145 Hiromitu Kashiwagi, Toyota all of Kuebrich Japan 3,568,723 3/1971 Sowards. 138/143 [73] Assignec: Toyota Jidosha Kogy o Kabn shiki FOREIGN PATENTS OR APPLICATIONS Kaisha, y h Aichi-ken, 2,075 5/1878 Great Britain 164/356 Japan [22] Filed: May 17, 1972 Primary Examiner-Francis S. Husar Assistant ExaminerV. K. Rising [211 App! 254228 Attorney, Agent, or Firm-Connolly & Hutz [30] Foreign Application Priority Data Jan. 17, 1972 Japan 47-6738 [57] ABSTRACT The present disclosure relates to a process for manu- [52] U.S. Cl 164/98, 164/100, 164/106, facturing cast pipes of the type which excel in heat- 164/112, 164/365, 164/369, 249/175, 249/96 insulating characteristics and which are highly durable [51] Int. Cl B22 19/00 under high temperatures. An internal core of metallic [58] Field of Search 164/356, 75, 98, 354, 411, material with high resistance to heat and corrosion is 164/100, 112 US, 110, 369, 365, 106; externally coated with a highly heat-insulating layer to 249/96, 175 thereby produce a double structure, and the double structure is then surrounded in molten metal to pro- [5 6] ReferencesCited duce the casting.

UNITED STATES PATENTS 4 Claims, 6 Drawing Figures 927,371 7/1909 Monnot 164/102 'PAIENTEDFEB' 4191s SHEU 1 [IF 2 FIG; I" FIIGLIZQ FIG. 4

FIG. '3

PROCESS FOR MANUFACTURING HEAT-INSULATED CASTINGS BACKGROUND OF THE INVENTION The present invention relates to a process for manufacturing heat-insulated castings.

In conventional methods for improving the heatinsulation quality of cast pipes, thepipe itself is fabricated of a material which is a poor heat conductor. Alternatively, cast pipes are lined with heat-insulating material or externally wrapped with such material. In some instances, pipes are fabricated so as to comprise a double structure of dissimilar materials.

In the conventional method of fabricating a pipe of material having poor heat conduction, non-metals are commonly used, particularly ceramics which are preferred in high temperature service. These ceramics lack toughness and cannot be used in service subjected from heavy vibration and impact load. In the case of applying a heat-insulator either internally or externally to the pipe, such an expedientis usually trouble-free if the configuration'of thepipe is simple. However, in the case of complex configurations this procedure is either very difficult or impossible. By externally wrapping the pipe with a heat-insulator, it is obviously impossible to protect the pipe from the heat source. In some instances a double pipe structure comprises a cast pipe with an internal layer of heat-insulating material, such as ceramic. However, when the liquid material passes through the pipe it is highly possible that the ceramic material will be dissolved or torn off.

SUMMARY OF THE INVENTION Accordingly, the present invention relates to a unique process for manufacturing heat-insulated castings to provide castings which avoid the disadvantages of the prior art and function in a trouble-free manner for extended periods of time.

In accordance with the present invention a process of manufacturing heat-insulated castings comprises the step of providing a metal core having resistance to heat and corrosion, and spreading a heat-insulating material on the outside of the core. The heat-insulating material is deposited onto the core and secured thereto by a bonding agent to thereby constitute a double structure with the core. The double structure is positioned in a mold with a cavity or space between the mold and the double structure. Molten metal is poured into the cavity to thereby surround the double structure in a metal casting.

The heat-insulating material may be selected from foamed alumina or fused silica, all of which are high in heat resistance and do not undergo any change at the melting temperature of cast iron. Moreover, the double structure may be positioned in a sand mold and molten metal vertically poured into the mold.

BRIEF DESCRIPTION OF THE DRAWING Novel features and advantages of the present invention in addition to those mentioned above will become apparent to those skilled in the art from a reading of the following detailed description in conjunction with the accompanying drawing wherein:

FIG. 1 is a perspective view of an internal core, according to the present invention;

FIG. 2 is a perspective view of a double structure comprising an internal core and an outer layer of heatinsulating material, according to the present invention;

FIG. 3 is a sectional'view illustrating the double structure of FIG. 2 positioned within a mold, according to the present invention;

FIG. 4 is a perspective view of a heat-insulated pipe produced according to the method of the present invention, with parts broken away to show detail;

FIG. 5 is a sectional view illustrating another double structure positioned within a mold, according to the present invention; and

FIG. 6 is a sectional view of still another double structure positioned within a mold, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring in more particularity to the drawing, the various figures illustrate an internal core I having an external heat-insulating layer 2. The layer is surrounded by a metal casting 3 which is accomplished through utilization of a mold 4. The present invention involves a manufacturing process of cast pipe wherein the pipe is easily produced ragardless of its shape. The process permits various surface treatments of the inside of the pipe and the thus produced product is highly heat resistant and durable. The resultant structure comprises a triple structure which allows passage of any liquid, gas, or solid, particularly those materials which would adversely affect standardly produced cast pipe.

The first step in the present method involves fabricating an internal core of metallic material which excels in its resistance to both heat and corrosion. Next, the core is coated with a highly heat-insulating material in layer form to thereby constitute a double structure with the core. The final step involves sheathing or otherwise surrounding the thus formed double structure with molten metal to thereby produce a casting having a triple structure comprising the core, the heat-insulating layer, and the outer metal sheath.

The present invention lends itself to pipe configurations which may be complicated in comparison to standard pipe configurations. In this regard, the core may be formed by shaping metal plates followed by welding or other joining techniques. Moreover, the internal core may be subjected to various surface treatments depending upon its ultimate use.

Concerning the heat insulating material to be applied to the internal core, ceramic materials have excellent heat-insulation qualities and may be selectively used as the heat-insulating material. Depending upon the type of heat-insulating material, drying orfiring may be required.

In the final step of surrounding the internal core and its external layer of heat-insulating material, the coated core is positioned in a mold and molten metal poured around the coated core to thereby surround the core with metal. Cast iron, aluminum alloys, and other casting materials may be provided to sheath the coated core. In cases where a core print is utilized, the print is removed from the casting after the metal solidifies. The finished product may be machined if desired.

Several examples according to the present invention are cited below.

EXAMPLE 1 As illustrated in FIG. l, a carbon-steel pipe 1 (JIS STPT35) for high temperature service measures 1.8 mm in wall thickness, 18 mm in outer diameter and 300 mm in length. A layer 2 of foamed alumina with a central grain size of 2 mm was applied over 150 mm of the central length of the pipe 1. For application of foamed alumina grains, a slurry consisting of ethyl silicate, ethyl alcohol, water and zircon flour was employed as the bonding agent. The applied alumina layer was dried at room temperature, gradually heated, dried at 250C. for hours, and then held at 500C. for 4 hours to dry.

The double structure pipe (FIG. 2) thus obtained was held in a C0 sand mold 4, as illustrated in FIG. 3, and a molten cast iron 3 (JIS FC at l,450C. was poured vertically into this mold to thereby yield a heatinsulated pipe, as shown in FIG. 4. In this case the wall thickness of cast iron 3 was about 10 mm.

EXAMPLE 2 A mild steel pipe similar to Example 1 was applied with a ZO-mesh fused silica. For the purpose of application, a slurry of colloidal silica and zircon flour was employed as the bonding agent. After the slurry was applied, the fused silica was spread thereon, and after drying the slurry was again applied, followed by a spreading of fused silica again. This process was repeated until a heat-insulating layer was formed at a thickness of about 3 mm.

The double structure thus obtained was dried in the same manner as in Example 1, and thereafter molten aluminum (JIS AC 28) was poured at 720C. by the gravity casting method. The casting obtained was about 5-6 mm in wall thickness.

EXAMPLE 3 Foamed polystyrene grains were applied to a thickness of 3 mm on the outside surface of a stainless steel (JIS SUS 27) pipe measuring 30 mm in outer diameter and 0.5 mm in wall thickness. For the purpose of application, a slurry of sodium silicate and zircon flour was employed as the bonding agent. The bonding agent slurry was applied first and then the foamed polystyrene grains were applied. This procedure was repeated until the foamed polystyrene grains were perfectly covered up with zircon flour. The applied layer was dried in the same manner as in Example 1. In the process of the drying, the foamed polystyrene was completely burned away, leaving a shell of zircon flour.

The double structure thus obtained was taken as the core and cast iron was poured in the same manner as in Example 1 to yield a casting of 3-4 mm in wall thickness.

EXAMPLE 4 An 0.8 mm thick stainless steel (JIS SUS 27) plate was press-formed, as shown in FIG. 5. Two pieces of the plate were welded together into a 120 mm long pipe 1 having a complicated profile and a mild steel piece 5 was tack-welded to the pipe 1 to serve as the core print.

Next, fused silica 2 was applied at a thickness of 4 mm to the body of the pipe 1 and dried.

The double structure thus obtained was held, as shown in FIG. 5, in a sand mold 4, and molten cast iron 3 (JIS FC 25) was poured at l,450C. to form a casting sheath. After casting, the core print 5 was removed to yield the end product, i.e., a heat-insulated pipe.

The wall thickness of the casting 3 was 3-4 mm minimum and 8-12 mm maximum.

EXAMPLE 5 A stainless steel (JIS SUS 27) pipe having a 32 mm bore and an 8 mm wall thickness was bulge-formed into a square, mm long pipe 1, with a bent angle of 60 R, as shown in FIG. 6. The bulge-formed pipe 1 was Cu-plated and applied on its outside surface with a fused silica 2 to a thickness of 2 mm. The assembly was then dried.

The double structure stainless steel pipe 1 thus obtained was filled with molding sand 6, and the filled pipe taken as the core was set in a sand mold 4, as illustrated in FIG. 6. A molten aluminum alloy 3 (JIS AC 48) was poured at 700C. around the core to form a sheath casting. After casting, the core sand 6 was removed, and after machining, the end product was obtained.

EXAMPLE 6 An alumina layer was deposited to a thickness of 0.3 mm by plasma spraying on the outside surface of a bulge-formed pipe manufactured in the same manner as in Example 5 to make a double structure. The thus obtained double structure pipe was filled with CO molding sand. Taking the filled double structure as the core, the same process as in Example 5 was executed to sheath it in a cast iron (JIS FCD 45) casting at l,450C., thereby yielding the end product.

As seen from the above examples, a variety of metallic materials can be utilized in the production of the internal core. Also, if necessary or desired, the metallic materials may be subjected to surface treatment of one type or another. The metallic material should be less heat-conductive and more resistant to heat and corrosion. Obviously, better results will be obtained if the selection of the material is made with full consideration of its service conditions. In order to minimize the heat lost through absorption by metal and thereby enhance the heat-insulation effect, the material should be as thin as possible in which case the initial temperature rise will be rapid although it will take less time to reach high temperatures. Obviously, the lower limit of thickness of the internal core must be such that it is durable and not easily damaged. In the case of a complicated internal core profile it can be produced with relative ease by bulge-forming or press-forming.

When the heat-insulating layer is deposited by the method explained above in the examples, selection of a particular material and the thickness thereof primarily depend upon factors associated with the particular use of the end product.

The thickness of the metal casting on the outside of the double structure may be similar to thicknesses obtained in common casting processes. Usually, this thickness will be approximately 3 mm when the gravity casting process is utilized. If it is desired to make the metal cast sheath thinner, other processes may be utilized, for example, the die cast process or the low pressure cast process.

Little, if any, casting defects occur with the method of the present invention, and quality is quite high. For the most part, the castings are free of defects such as cavity, porosity, casting crack, or blow hole. Since ing method described above in the examples is utilized,

separation of the core from the heat-insulating layer does not occur and no wide cracks are developed in the heat-insulating layer. 7

Also, another advantage of the present invention is that the double structure is utilized as the core for the molten metal thereby eliminating the necessity ofa separate core of the type used in producing standard cast pipe. Moreover, elimination of the above mentioned casting defects may also be attributed to the application of molten metal to a fully dried heat-insulating material.

A casting produced by the present method has excellent heat-insulation and the various materials and thicknesses of the core, heat-insulating material, and metal mey be selected to provide the best results for the particular application of the ultimately produced product. Moreover, complicated pipe profiles may be easily produced with the-method of the present invention. Durability of the finally produced product is vastly improved in comparison to existing pipe, and these improvements are the result of core material quality, wall thicknesses and surface treatments. Obviously, solids, liquids and gases may be passed through the pipe produced by the present method. We claim:

1. A process for manufacturing heat-insulated castings comprising the steps of providing a hollow metal core having resistance to heat and corrosion, applying a bonding agent to the outside of the core and thereafter coating a foamed alumina onto the bonding agent on the outside of the metal core, drying the thus obtained double structure at room temperature, and then at a temperature of approximately 250C. for at least about 10 hours followed by drying at about 500C. for several hours, positioning the double structure in a mold, and pouring molten metal into the mold to surround the double structure in a metal casting.

2. A process for manufacturing heat-insulated castings as in claim 1 wherein the double structure is positioned in a sand mold and the molten metal is poured vertically into the mold to thereby fill the cavity between the double structure and the sand mold.

3. A process for manufacturing heat-insulated castings comprising the steps of providing a hollow metal core having resistance to heat and corrosion, applying a bonding agent to the outside of the core and thereafter applying several times repeatedly aslurry consisting of sodium silicate and zircon flour as the bonding agent on the outside of the metal core on which a foamed polystyrene is spread, drying the thus obtained double structure at room temperature, and then at a temperature of approximately 250C. for at least about 10 hours followed by drying at about 500C. for several hours, positioning the double structure in a mold, and pouring molten metal into the mold to surround the double structure in a metal casting.

4. A process for manufacturing heat-insulated castings as in claim 3 wherein the double structure is positioned in a sand mold and the molten metal is poured vertically into the mold to thereby fill the cavity between the double structure and the sand mold. 

1. A PROCESS FOR MAUUFACTURING HEAT-INSULATED CASTINGS COMPRISING THE STEPS OF PROVIDING A HOLLOW METAL CORE HAVING RESISTANCE TO HEAT AND CORROSION, APPLYING A BONDING AGENT TO THE OUTSIDE OF THE CORE AND THEREAFTER COATING S FOAMED ALUMINA ONTO THE BONDING AGENT ON THE OUTSIDE OF THE METAL CORE, DRYING THE THUS OBTAINED DOUBLE STRUCTURE AT ROOM TEMERATURE, AND THEN AT A TEMPERATURE OF APPROXIMATELY 250*C. FOR AT LEAST ABOUT 10 HOURS FOLLOWED BY DRYING AT ABOUT 500*C. FOR SEVERAL HOURS, POSITIONING THE DOUBLE STRUCTURE IN A MOLD, AND POURING MOLTEN METAL INTO THE MOLD TO SURROUND THE DOUBLE STRUCTURE IN A METAL CASTING.
 2. A process for manufacturing heat-insulated castings as in claim 1 wherein the double structure is positioned in a sand mold and the molten metal is poured vertically into the mold to thereby fill the cavity between the double structure and the sand mold.
 3. A process for manufacturing heat-insulated castings comprising the steps of providing a hollow metal core having resistance to heat and corrosion, applying a bonding agent to the outside of the core and thereafter applying several times repeatedly a slurry consisting of sodium silicate and zircon flour as the bonding agent on the outside of the metal core on which a foamed polystyrene is spread, drying the thus obtained double structure at room temperature, and then at a temperature of approximately 250*C. for at least about 10 hours followed by drying at about 500*C. for several hours, positioning the double structure in a mold, and pouring molten metal into the mold to surround the double structure in a metal casting.
 4. A process for manufacturing heat-insulated castings as in claim 3 wherein the double structure is positioned in a sand mold and the molten metal is poured vertically into the mold to thereby fill the cavity between the double structure and the sand mold. 